The invention relates to sound reproduction and, in particular, provides improved loudspeakers, components and methods pertaining thereto. The invention has application, by way of non-limiting example, in sound reproduction of the type required by woofer and subwoofer drivers and loudspeakers.
A large percentage of loudspeakers used in audio systems are electrodynamic speakers. Such speakers employ a magnetic “motor” to produce movement of a cone-shaped diaphragm which, in turn, causes sound. The cone is typically disposed within a frame (or basket), with the wide end of the cone coupled to the frame by way of flexible membrane, called a suspension or surround, which axially centers the cone within the frame, yet, allows to move back and forth at audio frequencies. The narrow end of the cone is coupled to the frame by another flexible membrane, called a spider, which also helps to axially center the moving diaphragm.
The motor is made up of a voice coil, which is disposed (usually) behind the narrow end of the cone, and a magnetic circuit, which is disposed adjacent to and/or partially surrounding the coil. In operation, electrical audio signals from an amplifier (or other source) are applied to the voice coil, producing a varying electromagnetic field. This interacts with the magnetic field of the magnet circuit, causing the voice coil to move.
Because the voice coil is coupled to the diaphragm, its movement causes the diaphragm to pump in and out—explaining why the diaphragm and coil are sometimes referred to as a “piston.” That, in turn, causes air around the speaker to pressurize and depressurize, producing sound waves. To prevent sound waves omitted from the rear of the diaphragm from canceling those emitted from the front, the speakers are usually mounted within an enclosure.
Traditionally, speakers are divided into three categories: woofer, midrange and tweeter. The woofer reproduces low frequency (bass) sound ranging from about 20 to 3000 Hz. The midrange speaker reproduces a broad spectrum of sound, typically from about 1000 Hz to 10 kHz. The tweeter speaker reproduces high frequency (treble) sound ranging from about 4 to 20 kHz. In home audio systems, the woofer, midrange and tweeter are often housed in a single enclosure, as in the case of free-standing or floor speaker configurations. Where space is a consideration, the functions of the woofer and midrange may be combined in a single speaker, as in the case with bookshelf-sized speaker configurations.
In the last few decades, a new category (or sub-category) of speaker had come to the fore, the sub-woofer. Though definitions vary, these are designed to reproduce sounds in the range of 20 to 150 Hz, i.e., in the low end of what was traditionally the woofer range. Subwoofers are finding increased use throughout the home. In home theater applications, their increased bass response lends to a more authentic movie theater-like feel. In computer applications, they provide, in addition to improved overall frequency response, a convenient location for housing amplification circuitry used by satellite speakers that provide mid- and high-range reproduction. In more traditional home stereo applications, subwoofers add increased punch and/or fidelity to many musical genre.
Subwoofers available today suffer from any number of shortcomings. Depending on design, they may be to boomy; suffer roll-off at the lowest frequencies; consume excessive power; produce an overly a “dry” sound; and/or be too large for practical use. Although the art has made strides toward minimizing these problems, there remains a need for a compact, low-cost, high fidelity loudspeaker that can be easily installed and operated.
An object of this invention is to provide such loudspeakers.
More generally, an object of the invention is to provide improved apparatus and methods for sound reproduction and, specifically, improved loudspeakers and systems.
Another object is to provide such loudspeakers and methods as are particularly suited for reproducing low frequency sounds, e.g., as low as 20 Hz (or lower), for use in home theater, high fidelity, computer and other applications.
A further object of the invention is to provide loudspeakers with desired response characteristics, yet, of minimal size.
Yet another object is to provide such loudspeakers that can be easily connected with receivers, amplifiers, computers or other sound-producing equipment.
Still another object is to provide such loudspeakers that can be easily and safely interconnected with existing power sources.